A breathable roof underlay for cold and warm roof applications Vent3 Classic is a triple layer fabric, high performance breather membrane, made from high tensile spun bonded polypropylene layers, around a micro-porous polypropylene film. Designed for use in a fully supported or unsupported tiled, slated or metal roof system. The high vapour permeability and waterproof nature of the membrane, combined with excellent tensile/tear strength and high wind uplift resistance make Vent3 Classic the professional’s choice as the ultimate breather membrane.